1. Filed of the Invention
The present invention is related to a protection circuit and a method of operating a protection circuit.
2. Related Art
There are usually two types of short-circuit or over-current protection circuit: the one uses current-restricting circuit for protection and the other detects the temperature of the components for selecting protection scheme. The latter cannot achieve effective protection when the temperature surges so rapidly that the protecting scheme is not timely activated and the components are burnt without protection. Traditional methods of using current-restricting for protection may cause restriction to normal current pulses and end up with malfunctions.
Please refer to FIG. 1A, which is a schematic diagram illustrating a unit gain amplifier circuit known to the art. The unit gain amplifier circuit 10 includes a unit gain amplifier 11, a signal source 12 and a loading circuit 13. The signal source 12 generates a voltage Vin1 which is transmitted to the positive input terminal in1+. The output terminal out1 of the unit gain amplifier 11 is coupled to the negative input terminal in1− thereof and the loading circuit 13. An output current Iout1 and an output voltage Vout1 are outputted from the output terminal out1.
Refer to FIG. 1B, which is a schematic diagram of the wave form of the outputs of the unit gain amplifier circuit 10. It is observed that an upward pulse PL1 with a duration T1 and a downward pulse PL2 with a duration T2 occur in the output current Iout1 and the output voltage Vout1 respectively. Furthermore, it is also observed that a downward pulse PL3 with a duration T3 and an upward pulse PL4 with a duration T4 occur in the output current Iout1 and the output voltage Vout1 respectively.
If the durations T1, T2, T3 and T4 are short periods of time, those pulses will damage neither the unit gain amplifier 10 nor the loading circuit 13. Therefore, malfunctions may occur to the unit gain amplifier 10 known as prior art, if a traditional current restriction circuit is employed for the use of restricting currents.
Refer to FIG. 1C, which is a schematic diagram of a switching power circuit 20 known to the art. The switching power circuit 20 includes a signal source 21, an inductor L1, a loading circuit 22, a transistor X1, a diode D1 and a PWM controller 23, and generates output current Iout2 and output voltage Vout2, according to FIG. 1C. Similarly, pulses may occur in the output voltage Vout2 or the output current Iout2. If the durations of the pulses are short periods of time, no damage will occur to switching power circuit 20 or to the loading circuit 22.
Refer to FIG. 1D, which is a schematic diagram of an output stage circuit 31 known to the art. The output stage circuit 31 is coupled to a loading circuit 32 and generates an output current Iout3 and an output voltage Vout3. Compared with the circuits illustrated in FIGS. 1A and 1C, one may observe that the output stage circuit 31 may be considered as either the combination of the unit gain amplifier 11 and the signal source 12 or that of the signal source 21, the inductor L1, the loading circuit 22, the transistor X1, the diode D1 and the PWM controller 23. Any component in the output stage circuit 31 and the loading circuit 32 may be burnt down if the durations of pulses existing in either the output current Iout3 or the output voltage Vout3 are too long. On the contrary, malfunctions may occur if the durations of the pulses are very short and a traditional current restriction circuit is employed.
According to the above-mentioned, there is a need to develop a new protection circuit and protection method to avoid malfunctions when the circuit is under a normal operational condition and to restrict or shut-off the current to prevent the components from being damaged when the circuit is under an abnormal condition.